This invention relates to secondary batteries, and, in particular, to secondary batteries employing zinc electrodes. Conventional secondary batteries employing zinc electrodes such as, for example, silver-zinc and nickel-zinc alkaline batteries, exhibit a decline in cell capacity with continued cycling. This decline in cell capacity is attributable to the morphological changes, typically referred to as shape changes, which occur in the negative zinc battery electrode. The net effect of these shape changes is agglomeration and densification of the zinc electrode in the centre with a consequent reduction in surface area available for electrochemical reaction and formation of dendrites resulting in short circuiting.
A requirement is, however, that such cells and batteries must be cycled many times through discharge/charge cycles; leading in turn to several further requirements. The first is that the capacity of the rechargeable cell should not diminish significantly over a number of cycles, there should be no significant shape change particularly of the zinc electrode and no significant dendrite formation. Most especially, newly developed high energy density rechargeable zinc cells should be free or substantially free of toxicity, so as to be environmentally benign.
A number of additives were used in the past without much success. This invention presents the development of a product using which; the solubility of zinc in the electrolyte can be suppressed. A large number of people who have worked on this subject have failed and what was considered to be an insolvable problem has been solved due to this invention.